Epidermotropic malignant melanoma: the distinction between metastatic and new primary lesions in the skin.

Although there are scattered reports in the literature, little is known of the difficulties in reconciling the clinical and histologic findings in patients with malignant melanoma in whom more skin lesions develop in different areas after removal of the primary lesion. In some cases, what appears to be metastatic disease is, in reality, primary. In 33 biopsies from five patients with clinically metastatic disease, histologic examination showed metastatic disease in 12 specimens, new primary malignant lesions in 17 and atypical nevi in 4. The purpose of this paper is to define and discuss the difficulties in differentiating metastatic lesions from new primary malignant tumours.